1. Field of the Invention
The present invention generally relates to a driving force control apparatus for a vehicle. More specifically, the present invention relates to a driving force control apparatus that prevents degradation of acceleration performance and the occurrence of large torque shock when shifting from the non-execution to the execution of a driving force control operation.
2. Background Information
Japanese Laid-Open Patent Publication No. 2000-79838 describes a driving force control apparatus that sets a target driving force based on the driving conditions of a vehicle and controls the torque generated by the engine such that this target driving force is achieved. In this publication, the driving force control operation is not executed when the idle switch is ON because there are regions where it is preferable in terms of operability not to execute driving force control operation, such as when the accelerator pedal has been released (the idle switch ON). When driving force control operation is not executed, the driving force outputted as a result of the engine torque obtained from the accelerator pedal depression amount and the engine speed is taken as a second target driving force. When the vehicle shifts to the execution of driving force control operation, the shifting target driving force is calculated using delay processing such that the target driving force shifts gradually from the second target driving force to a first target driving force that is established based on the driving conditions of the vehicle. As a result, the drive torque changes smoothly during shifting and large torque shock does not occur.
In view of the above, there exists a need for an improved driving force control apparatus for a vehicle. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discovered that several disadvantages occur when the drive torque is changed smoothly during shifting of the driving force control operation from the non-execution mode to the execution mode as a consequence of always calculating the target driving force using delay processing during the shifting.
Specifically, since a large driving force is required when a vehicle starts to move, the starting acceleration performance can be improved over that of a vehicle not equipped with a driving force control apparatus by setting the first target driving force, which is the target driving force used when in the driving force control execution mode, to a large value. However, with the aforementioned publication, the driving force control apparatus shifts from the non-execution mode to the execution mode when the accelerator pedal is depressed and the vehicle is made to start from a stopped condition in which the accelerator pedal was released. Consequently, the effect of improving the starting acceleration performance cannot be fully realized because it takes time for the shifting target driving force to reach the first target driving force.
Therefore, in addition to making the drive torque change smoothly during shifting of the driving force control operation from the non-execution mode to the execution mode so that large torque shock does not occur, this invention increases the shifting speed during starting in order to improve the starting acceleration performance.
The first invention is a vehicle driving force control apparatus comprising at least one sensing device, a determining section, a switching section, a first target driving force computing section, a first target torque computing section, a second target torque computing section, a selecting section, an engine output torque controlling device, a second target driving force computing section, a shifting target driving force computing section, and a shift controlling section. The at least one sensing device is configured to detect at least one driving condition of a vehicle. The determining section is configured to determine if a driving force control operation should be executed based on the at least one driving condition detected by the at least one sensing device. The switching section is configured to switch to between an execution mode and a non-execution mode of the driving force control operation based on a result of the determining section. The first target driving force computing section is configured to calculate a first target driving force based on the at least one driving condition detected by the at least one sensing device. The first target torque computing section is configured to calculate a first target torque based on the first target driving force and the at least one driving condition detected by the at least one sensing device. The second target torque computing section is configured to calculate a second target torque based on engine speed and the at least one driving condition detected by the at least one sensing device. The selecting section is configured to select the first target torque when the switching section switches to the execution mode of the driving force control operation and the second target torque when the switching section switches to the non-execution mode of the driving force control operation. The engine output torque controlling device is configured to control engine output torque based on which of the first and second target torques has been selected by the selection section. The second target driving force computing section is configured to calculate a second target driving force that is obtained when the second target torque has been selected by the selection section. The shifting target driving force computing section is configured to calculate a shifting target driving force to gradually shift from the second target driving force to the first target driving force when the driving force control operation is shifted from the non-execution mode to the execution mode. The shift controlling section is configured to switch from the second target driving force to the shifting target driving force when the driving force control operation is shifted from the non-execution mode to the execution mode. The shift controlling section is being further configured to increase shifting speed of the shifting target driving force in response to an increase in an accelerator pedal depression amount upon detection of the vehicle starting to move.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.